Problem: $\dfrac{9}{2} - \dfrac{4}{5} = {?}$
Answer: $ = {\dfrac{9 \times 5}{2 \times 5}} - {\dfrac{4 \times 2}{5 \times 2}} $ $ = {\dfrac{45}{10}} - {\dfrac{8}{10}} $ $ = \dfrac{{45} - {8}}{10} $ $ = \dfrac{37}{10}$